Alarm switch device



Se t. 8, 1953 F. H. TOWNSEND EIAL 2,651,687 ALARM SWITCH DEVICE FiledDec. 31, 1951 Inventor FEW/CA H. TOWN SEND flND- HIIRYEY S. HILL M, lAttorneys Patented Sept. 8, 1953 ALARM SWITCH DEVICE Frederick HenryTownsend and Harvey Sydney Hall, Cambridge, England, assignors toCathodeon Limited, Cambridge, England, a British company ApplicationDecember 31, 1951, Serial No. 264,302 In Great Britain October 25, 1951The present invention relates to alarm switch devices for completingelectrical circuits in the event of emergencies, more particularly tosuch devices that comprise an outer casing of frangible material havingan elongated tubular form closed at one end, a rod electrode enclosedwithin said outer casing and extending substantially coaxially of thecasing and for substantially the entire length thereof, and a coiledelectrode surrounding and spaced from the rod, the two electrodes beingadapted to be connected to a suitable electric circuit.

More specifically it is the object of the invention to provide a switchdevice of this kind which is positive in its operation and more emcientin use.

According to the invention there is provided an alarm switch device ofthe kind referred. to in which the end of the rod electrode at theclosed end of the outer casing is located in a block of insulatingmaterial to prevent lateral movement of the rod in the inoperative stateof the switch.

Preferably there is provided a second operating spring associated with acontact member electrically connected to the coiled electrode andsurrounding and spaced from the rod, together with a co-operatingcontact member on the rod, the spring being held under load and thearrangement being such that in the event of fracture of the outer casingand consequent removal of the lower half thereof, the loading of thespring is removed to bring about contact between the two contactmembers.

The detector device may be adapted to cooperate with a separate socketdevice mounted on a suitable surface or it may be incorporatedintegrally with a mounting containing appropriate terminals.

In a preferred embodiment the coiled electrode is in the form of aspring held under compression within the outer casing and the secondoperating spring is mounted in end-to-end relationship with it alsounder compression so that in the event of fracture of the outer casingby sideways impact, completely removing the lower part of the casing,the coiled electrode moves to remove the compressive loading of thesecond operating spring whereby the latter expands longitudinally toallow the contact member with which it is associated to contact theco-operating member on the rod electrode.

In order that the invention may be more clearly understood, referencewill now be made to the accompanying drawings which show certainspecific embodiments thereof by way of non-limiting example and in which11 Claims. (01. 200-52) Fig. 1 shows a section through one embodiment ofswitch used in conjunction with a separable mounting socket.

Fig. 2 shows a plan view along the line 22 of Fig. 1.

Fig. 3 shows a plan view along the line 33 of Fig. 1.

Fig. 4 shows a section through a second embodiment showing theincorporation of the device integrally with a mounting containingappropriate terminals.

Fig. 5 shows a plan view of Fig. 4.

Referring to the drawings, l represents the outer casing of the devicewhich is preferably made from glass. The casing is of tubular elongatedform closed at the lower end 2. At the upper end is provided a metalflange 3 which acts as a seating for centralising metal mounting t forthe metal rod electrode 5. The rod 5 is mounted in the mounting 4 bymeans of a glass bead 1 which is sealed to the mounting 4 and to therod.

The other end of the rod 5 is held and located by the member 8 of theinsulating material.

Surrounding the rod 5 is a coiled electrode 9 in the form of a springwhich bears at one end on a metal cup I0 centralised on the member 8 bytags I I. The base of the cup is apertured at E2 to allow the rod 5 topass into the aperture It in the member 8. The aperture I2 issufficiently large to clear the rod 5. At the other end of the springelectrode 9 is a further cup I4 having shoulders I 5 preventing inwardmovement of the electrode 9. The cup I4 also has an aperture [6suiiiciently large to clear the rod 5.

The cup I4 is accommodated within another cup I! having flanges I8preventing outward movement of electrode 9 and the cup I? also forms amounting for a second operating spring 59 which is mounted between theshoulder 29 on the cup I! and the underside of mounting 4.

The cup I1 is provided with a constricted shoulder 2| which acts as acontact member for cooperation with contact 22 secured to the rod 5, aswill be explained later.

The rod 5 is also provided with a further contact 23 near its other endas shown.

The mounting 4 is surrounded by a threaded portion 24 for co-operationwith the socket shown in Figs. 2 and 3, underneath which is positioned ametal washer 6.

In assembling the device, the parts 3, 5 and 2d are connected together,e. g. by soldering and the springs 9 and I9 are of such normal lengththat they must be compressed for insertion into the casing l. The metalflange 3 is hermetically sealed on to the casing l whereby the ingressof moisture into the device is prevented so as to avoid risk ofcorrosion of the metal parts. A suitable termination for the rod 5 isshown at 25.

A suitable socket for the device of Fig. l is shown in Figs. 2 and 3.The socket comprises a body 26 of suitable material such as metal havinga mounting flange 2'? for attachment to a suitable surface, e. g. byscrews passing through apertures 22"; therein.

An insulated bush 29 lines the body 26 and is prevented from turningtherein by a suitable key 3% situated at the base thereof fittingclosely in aperture 3! in the body. The bush 2?) locates a spring 32which itself is prevented from turning in the bush by forming one endwith a radiallyprojecting portion 33 fitting in a slot 34 cut in thebush 29 from its top to the key 30.

The spring 32 is adapted to receive the switch device. The pitch of thespring is less than the pitch of the threads on the threaded portion 24,so that when the switch is screwed into the socket the spring is placedunder tension thereby ensuring good connection between the parts and 42.

t the same time it forms a convenient means of reducing the transmissionto the switch of any vibrations of the surface on which the device ismounted. The washer 5 causes the end of the spring d2 to jam in the topof the thread in member 2 before the radially-projecting portion 33comes up against the bottom of the slot 3a in the bush 29.

The upper end of spring 32 has a projecting portion 35 soldered to aterminal member 36 located in a recess 3? in a terminal block 38 ofinsulating material. The latter has a further recess 39 accommodating asecond terminal 43 soldered to lead M which goes to a centre contactstud 52 located in a recess 43 in the underside of block 38. The twoterminals 35 and ill are soldered to 35 and M respectively therebysecuring them in position and providing electrical connection. 323 andit respectively to clamp external circuit leads.

The block 38 is secured to the body 26 by screws ii (see Fig. 4). Arubber washer 48 separates the block 38 and the body 26.

Channels 4 9 and 5B are made in the block 38 for electrical leads to theterminals 35 and 4B. These channels 4%}, 50 are provided with rubberseals 5!, 5 2 located in suitable recesses, through which externalcircuit leads are connected to the terminals. This forms a convenientmeans of waterproofing the lead entry.

The block 38 also has screw holes 53 for affixing a cover plate 56. Arubber washer 55' is interposed between the cover plate 5 and the block38.

The switch device is screwed into the spring 32 and a cover 56 isengaged over it. The cover is of metal and has threads 5i to engagethreads 58 on the outside of body 26. A rubber gasket 59 serves tocushion and support the switch and provide waterproofing.

There is thus electrical continuity between terminal 36, spring 32,threads 24, mounting 4, spring l9, cup ll, cup M, spring electrode 9 andcup In, and between terminal Ml, contact stud 42, terminal 25, rod 5 andcontacts 22 and 23.

To operate the switch it is only necessary to strike a blow on thecasing i from any direction. If the blow is sideways, acting to removecompletely the lower part of the glass casing, there will be no supportfor the compressed coil spring Screws M and 35 are provided in terminalselectrode 9 which will thus expand and remove its support from thesecond operating spring Hi. The latter will move longitudinally untilcontact shoulder 2! strikes contact member 22 on the rod 5 establishingelectrical contact between terminals 3% and 60 by the electricallyconducting paths set out above. Thus, if the terminals 36 and 40 beconnected in a suitable alarm circuit, breaking of the casing I willinstitute an alarm.

If the blow on the casing I be end-on, crushing the glass in alongitudinal compressing action, the spring 9 will be further compresseduntil the cup ii] strikes the contact 23 thereby establishing electricalcontinuity over the paths provided.

If the blow be a sideways one, it is feasible that no longitudinalmovement of the contacts is possible but the sideways pressure willcause contact to be made between the coiled spring electrode 9 and therod electrode 5.

Figs. 4 and 5 show an embodiment of the switch incorporating its ownmounting and terminals as an integral structure.

All the operating parts are the same as the embodiment of Fig. l andhave the same reference numerals. The closure devices for the upper endof the case are, however, difierent to provide for the integralmounting.

Surrounding the metal mounting 4 is an annular closure member Ell havinga radially extending flange 6!. This flange provides a mounting bracketfor the device and to this end is provided with apertures 82 for thepassage of screws or the like. The member 66 is soldered to the mountinga.

The rod 5 is connected by a lead st to an external terminal 65. Theupper portion of the device as now constituted is placed in a suitablemould that grips the edges of the flange 6! and a synthetic resinmaterial is poured in which, when set, produces a block 66 of insulatingmaterial that seals off the upper portion completely, suitably embeddingthe terminal 65. The mould has a suitable plug to form a recess 6'! forconnection of a suitable lead to the terminal which is threaded at 68for a fixing screw.

In use the flange 6! acts as one terminal so that the device can besecured to a suitable metal fixing to which one lead of the alarmcircuit is made, the other lead being taken to terminal 65.

The operation of the device of Figs. 4 and 5 is precisely the same asthat of Fig. 1.

The invention thus provides an extremely simple alarm switch operable bybreaking the casing I. It may, therefore, be used as a crash-detectorswitch for vehicles, particularly aircraft, when it could be secured tothe craft to depend downwards immediately behind the outer skin or evenexternally from its body to effect actuation of an alarm circuit onimpingement. The alarm circuit may comprise a simple warning signaldevice such as a lamp or buzzer or, preferably for this purpose, it maycomprise a fire-fighting installation whereby a crash landing willautomatically actuate fire-prevention or fire-fighting devices, such assprays for fire-extinguishing compounds.

Alternatively, of course, the device may merely be mounted in a wall andconnected to suitable warning circuits so that it may be used as anemergency signal device.

In order to be able to test the installation, the rod 5 may have aconnection such as that shown at 69 in Fig. l. The connection 69 issealed into and through the wall of the cover I to project externally atiii. If then a connection be made externally of the device between point10 and the flange 6|, the circuit in which the device is connected willbe completed whereby continuity of the circuit and effectiveness thereofmay be rapidly tested.

We claim:

1. An alarm switch device for completing electrical circuits in theevent of emergencies comprising an outer casing of frangible materialhaving an elongated tubular form closed at one end, a rod electrodeenclosed within said outer casing and extending substantially coaxiallyof the easing and for substantially the entire length thereof, a coiledelectrode surrounding and spaced from said rod electrode, a block ofinsulating material supported by the closed end of said frangibleenvelope. means for locating said rod electrode in said block ofinsulating material out of contact with said coiled electrode, anexternal contact on said casing, means for connecting said externalcontact to said coiled electrode, said rod electrode being sealed intobut projecting out of said casing, and sealing means for hermeticallysealing said casing against the ingress of fluids and gases.

2. An alarm switch device as claimed in claim 1, in which the externalcontact is a screw thread and the projecting rod electrode is arrangedcoaxially with it.

3. An alarm switch device comprising a socket, two terminal contacts insaid socket, an external screw thread on said socket, a demountableswitch removably engaging in said socket and comprising an outer casingof frangible material having an elongated tubular form closed at oneend, a rod electrode enclosed within said outer casing and extendingsubstantially coaxially of the casing and for substantially the entirelength thereof, a coiled electrode surrounding and spaced from said rod,a block of insulating material supported within said frangible casing atthe closed end thereof, means for locating said rod electrode in saidinsulating block out of contact with said coiled electrode, contactmeans externally of said casing connected respectively to said twoelectrodes, said contact terminals in said socket being positioned forcontact with said two external contacts on said switch device casingwhen said switch device is mounted within said socket, a closure devicecomprising a cap centrally apertured and having an internal screw threadso located and arranged that said closure device may be slipped oversaid casing protruding from said socket to allow the threads internallyarranged on said closure device to engage over the threads externallyarranged on said socket, and a flexible gasket arranged between the endof said socket and the interior of said closure device to cushion saiddemountable switch within said socket and closure device assembly.

4. An alarm switch device comprising a socket, two terminal contacts insaid socket, a demountable switch removably engaging in said socket andcomprising an outer casing of frangible material having an elongatedtubular form closed at one end, a rod electrode enclosed within saidouter casing and extending substantially coaxially of the casing and forsubstantially the entire length thereof, a coiled electrode surroundingand spaced from said rod, a block of insulating material supportedwithin said frangible casing at the closed end thereof, means forlocating said rod electrode in said insulating block, and contact meansexternally of said casing connected respectively to said two electrodes,said contact terminals in said socket being positioned for contact withsaid two external contacts on said switch device casing when said switchdevice is mounted within said socket.

5. An alarm switch device as claimed in claim 4, comprising a coilspring in said socket, locating means in said socket for locating saidspring therewithin, and means connecting said coil spring to one of saidcontact terminals in said socket.

6. An alarm switch device as claimed in claim 4, comprisingelectrically-conducting external screw thread means on said frangiblecasing adapted to engage within the convolutions of said coil spring insaid socket, said screw thread on said frangible casing comprising anexternal terminal connected to one of said electrodes within saidcasing.

7. An alarm switch device for completing electrical circuits in theevent of emergencies comprising an outer casing of frangible materialhaving an elongated tubular form closed at one end, a rod electrodeenclosed Within said outer casing and extending substantially coaxiallyof the easing and for substantially the entire length thereof, a coiledelectrode surrounding and spaced from said rod electrode, a block ofinsulating material supported b the closed end of said frangibleenvelope, means for locating said rod electrode in said block ofinsulating material out of contact with said coiled electrode, a metalclosure cap for the open end of said frangible casing, means forconnecting said cap to said coiled electrode, a mounting flangeassociated with said cap, said rod electrode being sealed into butprojecting out of said casing out of contact with said cap, a terminalfor external connection connected to said projecting rod electrode, anda block of insulating material moulded around said cap and terminal andover said flange but allowing a portion of said flange to protrude formounting purposes and leaving exposed a portion of said terminal forexternal connection.

8. An alarm switch device as claimed in claim 7, and comprising furthera second operating spring, a first contact member electrically connectedto said coiled electrode within said casing, said operating spring beingassociated with said contact member and surrounding and spaced from saidrod electrode, a second cooperating contact member on said rod locatednormally out of contact with said first contact member and means fornormally holding said second operating spring under load, whereby in theevent of fracture of the frangible casing the loading of said operatingspring is removed to bring about contact between said two contactmembers.

9. An alarm switch device for completing electrical circuits in theevent of emergencies comprising an outer casing of frangible materialhaving an elongated tubular form closed at one end, a rod electrodeenclosed within said outer casing and extending substantially coaxiallyof the casing and for substantially the entire length thereof, a coiledelectrode surrounding and spaced from said rod electrode, means forlocating said rod electrode out of contact with said coiled electrode,an operating spring, a first contact member electrically connected tosaid coiled electrode Within said casing, said operating spring beingassociated with said first contact member and surrounding and spacedfrom said rod electrode, a second cooperating contact member on said rodlocated normally out of contact with said first contact member, andmeans for normally holding said second operating spring under loadwhereby in the event of fracture or the frangible casing the loading ofsaid operating spring is removed to bring about contact between saidfirst and said second contact members, an external contact on saidcasing, means for connecting said external contact to said coiledelectrode, said rod electrode being sealed into but projecting out ofsaid casing, and sealing means for hermetically sealing said casingagainst the ingress of fluids.

10. An alarm switch device comprising a socktwo terminal contacts insaid socket, an external screw thread on said socket, a demountableswitch removably engaging in said socket and comprising an outer casingof frangible material having an elongated tubular form closed at oneend, a rod electrode enclosed within said outer casing and extendingsubstantially coaxially of the casing and for substantially the entirelength thereof, a coiled electrode surrounding and spaced from rod, ablock of insulating material supported within said frangible casing atthe closed end thereof, means for locating said rod electrode in saidinsulating block out of contact with said coiled electrode, an operatingspring, a first contact member electrically connected to said coiledelectrode within said casing, said operating spring being associatedwith said first contact member and surrounding and spaced from said rodelectrode, a second cooperating contact member on said rod locatednormally out of contact with said first contact member, and means fornormally holding said second operating spring under load whereby in theevent of fracture of the frangible casing the loading of said operatingspring is removed to bring about contact between said first and saidsecond contact members, contact means externally of said casingconnected respectively to said two electrodes, said contact terminals insaid socket being positioned for contact with said two external contactson said switch device casing when said switch device is mounted withinsaid socket, a closure device comprising a cap centrally apertured andhaving an internal screw thread so located and arranged that saidclosure device may be slipped over said casing protruding from saidsocket to allow the threads internally arranged on said closure deviceto engage over the threads externally arranged on said socket, and aflexible gasket arranged between the end of said socket and the interiorof said closure device tocushion said demountable switch within saidsocket and closure device assembly.

11. An alarm switch device comprising a socket, two terminal contacts insaid socket, a demountable switch removably engaging in said socket andcomprising an outer casing of frangible material having an elongatedtubular form closed at one end, a rod electrode enclosed within saidouter casing and extending substantially coaxially .of the casing andfor substantially the entire length thereof, a coiled electrodesurrounding and spaced from saidrod, a block of insulating materialsupported within said frangible casi g at the closed end thereof, meansfor locating said rod electrode in said insulating block, an operatingspring, a first contact member electrically connected to said coiledvelectrode within said casing, said operating spring being associatedwith said first contact member and surrounding and spaced from said rodelectrode, a second cooperating contact member on said rod locatednormally out of contact with said first contact member, and means fornormally holding said second operating spring under load whereby in theevent of fracture of the frangible casing the loading of said operatingspring is removed to bring about contact between said first and saidsecond contact members, and contact means externally of said casingconnected respectively tosaid two electrodes, said contact terminals insaid socket being positioned for contact with said twoexternal contactson said switch device casing when said switch device is mounted withinsaid socket.

FREDERICK HENRY TOWNSEND. HARVEY SYDNEY HALL.

Name Date Graham et al Apr. 24, 1917 Number

